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09444a2e76
systemd/tools/elf2efi.py
Daan De Meyer 09444a2e76 elf2efi: Make compatible with python 3.6 again 
CentOS 8 ships python 3.6 so let's try and stay compatible with that
since the only feature we're using that requires python 3.9 is the
streamlined type annotations which are trivial to convert back to
the older stuff to stay compatible with python 3.6.
2023-07-14 14:41:19 +02:00

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#!/usr/bin/env python3
# SPDX-License-Identifier: LGPL-2.1-or-later
# Convert ELF static PIE to PE/EFI image.
# To do so we simply copy desired ELF sections while preserving their memory layout to ensure that
# code still runs as expected. We then translate ELF relocations to PE relocations so that the EFI
# loader/firmware can properly load the binary to any address at runtime.
#
# To make this as painless as possible we only operate on static PIEs as they should only contain
# base relocations that are easy to handle as they have a one-to-one mapping to PE relocations.
#
# EDK2 does a similar process using their GenFw tool. The main difference is that they use the
# --emit-relocs linker flag, which emits a lot of different (static) ELF relocation types that have
# to be handled differently for each architecture and is overall more work than its worth.
#
# Note that on arches where binutils has PE support (x86/x86_64 mostly, aarch64 only recently)
# objcopy can be used to convert ELF to PE. But this will still not convert ELF relocations, making
# the resulting binary useless. gnu-efi relies on this method and contains a stub that performs the
# ELF dynamic relocations at runtime.
# pylint: disable=missing-docstring,invalid-name,attribute-defined-outside-init
import argparse
import hashlib
import io
import os
import pathlib
import time
import typing
from ctypes import (
c_char,
c_uint8,
c_uint16,
c_uint32,
c_uint64,
LittleEndianStructure,
sizeof,
)
from elftools.elf.constants import SH_FLAGS
from elftools.elf.elffile import ELFFile, Section as ELFSection
from elftools.elf.enums import (
ENUM_DT_FLAGS_1,
ENUM_RELOC_TYPE_AARCH64,
ENUM_RELOC_TYPE_ARM,
ENUM_RELOC_TYPE_i386,
ENUM_RELOC_TYPE_x64,
)
from elftools.elf.relocation import (
Relocation as ElfRelocation,
RelocationTable as ElfRelocationTable,
)
class PeCoffHeader(LittleEndianStructure):
_fields_ = (
("Machine", c_uint16),
("NumberOfSections", c_uint16),
("TimeDateStamp", c_uint32),
("PointerToSymbolTable", c_uint32),
("NumberOfSymbols", c_uint32),
("SizeOfOptionalHeader", c_uint16),
("Characteristics", c_uint16),
)
class PeDataDirectory(LittleEndianStructure):
_fields_ = (
("VirtualAddress", c_uint32),
("Size", c_uint32),
)
class PeRelocationBlock(LittleEndianStructure):
_fields_ = (
("PageRVA", c_uint32),
("BlockSize", c_uint32),
)
def __init__(self, PageRVA: int):
super().__init__(PageRVA)
self.entries: typing.List[PeRelocationEntry] = []
class PeRelocationEntry(LittleEndianStructure):
_fields_ = (
("Offset", c_uint16, 12),
("Type", c_uint16, 4),
)
class PeOptionalHeaderStart(LittleEndianStructure):
_fields_ = (
("Magic", c_uint16),
("MajorLinkerVersion", c_uint8),
("MinorLinkerVersion", c_uint8),
("SizeOfCode", c_uint32),
("SizeOfInitializedData", c_uint32),
("SizeOfUninitializedData", c_uint32),
("AddressOfEntryPoint", c_uint32),
("BaseOfCode", c_uint32),
)
class PeOptionalHeaderMiddle(LittleEndianStructure):
_fields_ = (
("SectionAlignment", c_uint32),
("FileAlignment", c_uint32),
("MajorOperatingSystemVersion", c_uint16),
("MinorOperatingSystemVersion", c_uint16),
("MajorImageVersion", c_uint16),
("MinorImageVersion", c_uint16),
("MajorSubsystemVersion", c_uint16),
("MinorSubsystemVersion", c_uint16),
("Win32VersionValue", c_uint32),
("SizeOfImage", c_uint32),
("SizeOfHeaders", c_uint32),
("CheckSum", c_uint32),
("Subsystem", c_uint16),
("DllCharacteristics", c_uint16),
)
class PeOptionalHeaderEnd(LittleEndianStructure):
_fields_ = (
("LoaderFlags", c_uint32),
("NumberOfRvaAndSizes", c_uint32),
("ExportTable", PeDataDirectory),
("ImportTable", PeDataDirectory),
("ResourceTable", PeDataDirectory),
("ExceptionTable", PeDataDirectory),
("CertificateTable", PeDataDirectory),
("BaseRelocationTable", PeDataDirectory),
("Debug", PeDataDirectory),
("Architecture", PeDataDirectory),
("GlobalPtr", PeDataDirectory),
("TLSTable", PeDataDirectory),
("LoadConfigTable", PeDataDirectory),
("BoundImport", PeDataDirectory),
("IAT", PeDataDirectory),
("DelayImportDescriptor", PeDataDirectory),
("CLRRuntimeHeader", PeDataDirectory),
("Reserved", PeDataDirectory),
)
class PeOptionalHeader(LittleEndianStructure):
pass
class PeOptionalHeader32(PeOptionalHeader):
_anonymous_ = ("Start", "Middle", "End")
_fields_ = (
("Start", PeOptionalHeaderStart),
("BaseOfData", c_uint32),
("ImageBase", c_uint32),
("Middle", PeOptionalHeaderMiddle),
("SizeOfStackReserve", c_uint32),
("SizeOfStackCommit", c_uint32),
("SizeOfHeapReserve", c_uint32),
("SizeOfHeapCommit", c_uint32),
("End", PeOptionalHeaderEnd),
)
class PeOptionalHeader32Plus(PeOptionalHeader):
_anonymous_ = ("Start", "Middle", "End")
_fields_ = (
("Start", PeOptionalHeaderStart),
("ImageBase", c_uint64),
("Middle", PeOptionalHeaderMiddle),
("SizeOfStackReserve", c_uint64),
("SizeOfStackCommit", c_uint64),
("SizeOfHeapReserve", c_uint64),
("SizeOfHeapCommit", c_uint64),
("End", PeOptionalHeaderEnd),
)
class PeSection(LittleEndianStructure):
_fields_ = (
("Name", c_char * 8),
("VirtualSize", c_uint32),
("VirtualAddress", c_uint32),
("SizeOfRawData", c_uint32),
("PointerToRawData", c_uint32),
("PointerToRelocations", c_uint32),
("PointerToLinenumbers", c_uint32),
("NumberOfRelocations", c_uint16),
("NumberOfLinenumbers", c_uint16),
("Characteristics", c_uint32),
)
def __init__(self):
super().__init__()
self.data = bytearray()
N_DATA_DIRECTORY_ENTRIES = 16
assert sizeof(PeSection) == 40
assert sizeof(PeCoffHeader) == 20
assert sizeof(PeOptionalHeader32) == 224
assert sizeof(PeOptionalHeader32Plus) == 240
# EFI mandates 4KiB memory pages.
SECTION_ALIGNMENT = 4096
FILE_ALIGNMENT = 512
# Nobody cares about DOS headers, so put the PE header right after.
PE_OFFSET = 64
def align_to(x: int, align: int) -> int:
return (x + align - 1) & ~(align - 1)
def use_section(elf_s: ELFSection) -> bool:
# These sections are either needed during conversion to PE or are otherwise not needed
# in the final PE image.
IGNORE_SECTIONS = [
".ARM.exidx",
".dynamic",
".dynstr",
".dynsym",
".eh_frame_hdr",
".eh_frame",
".gnu.hash",
".hash",
".note.gnu.build-id",
".rel.dyn",
".rela.dyn",
]
# Known sections we care about and want to be in the final PE.
COPY_SECTIONS = [
".data",
".osrel",
".rodata",
".sbat",
".sdmagic",
".text",
]
# By only dealing with allocating sections we effectively filter out debug sections.
if not elf_s["sh_flags"] & SH_FLAGS.SHF_ALLOC:
return False
if elf_s.name in IGNORE_SECTIONS:
return False
# For paranoia we only handle sections we know of. Any new sections that come up should
# be added to IGNORE_SECTIONS/COPY_SECTIONS and/or the linker script.
if elf_s.name not in COPY_SECTIONS:
raise RuntimeError(f"Unknown section {elf_s.name}, refusing.")
if elf_s["sh_addr"] % SECTION_ALIGNMENT != 0:
raise RuntimeError(f"Section {elf_s.name} is not aligned.")
if len(elf_s.name) > 8:
raise RuntimeError(f"ELF section name {elf_s.name} too long.")
return True
def convert_elf_section(elf_s: ELFSection) -> PeSection:
pe_s = PeSection()
pe_s.Name = elf_s.name.encode()
pe_s.VirtualSize = elf_s.data_size
pe_s.VirtualAddress = elf_s["sh_addr"]
pe_s.SizeOfRawData = align_to(elf_s.data_size, FILE_ALIGNMENT)
pe_s.data = bytearray(elf_s.data())
if elf_s["sh_flags"] & SH_FLAGS.SHF_EXECINSTR:
pe_s.Characteristics = 0x60000020 # CNT_CODE|MEM_READ|MEM_EXECUTE
elif elf_s["sh_flags"] & SH_FLAGS.SHF_WRITE:
pe_s.Characteristics = 0xC0000040 # CNT_INITIALIZED_DATA|MEM_READ|MEM_WRITE
else:
pe_s.Characteristics = 0x40000040 # CNT_INITIALIZED_DATA|MEM_READ
return pe_s
def copy_sections(elf: ELFFile, opt: PeOptionalHeader) -> typing.List[PeSection]:
sections = []
for elf_s in elf.iter_sections():
if not use_section(elf_s):
continue
pe_s = convert_elf_section(elf_s)
if pe_s.Name == b".text":
opt.BaseOfCode = pe_s.VirtualAddress
opt.SizeOfCode += pe_s.VirtualSize
else:
opt.SizeOfInitializedData += pe_s.VirtualSize
if pe_s.Name == b".data" and isinstance(opt, PeOptionalHeader32):
opt.BaseOfData = pe_s.VirtualAddress
sections.append(pe_s)
return sections
def apply_elf_relative_relocation(
reloc: ElfRelocation, image_base: int, sections: typing.List[PeSection], addend_size: int
):
# fmt: off
[target] = [
pe_s for pe_s in sections
if pe_s.VirtualAddress <= reloc["r_offset"] < pe_s.VirtualAddress + len(pe_s.data)
]
# fmt: on
addend_offset = reloc["r_offset"] - target.VirtualAddress
if reloc.is_RELA():
addend = reloc["r_addend"]
else:
addend = target.data[addend_offset : addend_offset + addend_size]
addend = int.from_bytes(addend, byteorder="little")
# This currently assumes that the ELF file has an image base of 0.
value = (image_base + addend).to_bytes(addend_size, byteorder="little")
target.data[addend_offset : addend_offset + addend_size] = value
def convert_elf_reloc_table(
elf: ELFFile,
elf_reloc_table: ElfRelocationTable,
image_base: int,
sections: typing.List[PeSection],
pe_reloc_blocks: typing.Dict[int, PeRelocationBlock],
):
NONE_RELOC = {
"EM_386": ENUM_RELOC_TYPE_i386["R_386_NONE"],
"EM_AARCH64": ENUM_RELOC_TYPE_AARCH64["R_AARCH64_NONE"],
"EM_ARM": ENUM_RELOC_TYPE_ARM["R_ARM_NONE"],
"EM_LOONGARCH": 0,
"EM_RISCV": 0,
"EM_X86_64": ENUM_RELOC_TYPE_x64["R_X86_64_NONE"],
}[elf["e_machine"]]
RELATIVE_RELOC = {
"EM_386": ENUM_RELOC_TYPE_i386["R_386_RELATIVE"],
"EM_AARCH64": ENUM_RELOC_TYPE_AARCH64["R_AARCH64_RELATIVE"],
"EM_ARM": ENUM_RELOC_TYPE_ARM["R_ARM_RELATIVE"],
"EM_LOONGARCH": 3,
"EM_RISCV": 3,
"EM_X86_64": ENUM_RELOC_TYPE_x64["R_X86_64_RELATIVE"],
}[elf["e_machine"]]
for reloc in elf_reloc_table.iter_relocations():
if reloc["r_info_type"] == NONE_RELOC:
continue
if reloc["r_info_type"] == RELATIVE_RELOC:
apply_elf_relative_relocation(
reloc, image_base, sections, elf.elfclass // 8
)
# Now that the ELF relocation has been applied, we can create a PE relocation.
block_rva = reloc["r_offset"] & ~0xFFF
if block_rva not in pe_reloc_blocks:
pe_reloc_blocks[block_rva] = PeRelocationBlock(block_rva)
entry = PeRelocationEntry()
entry.Offset = reloc["r_offset"] & 0xFFF
# REL_BASED_HIGHLOW or REL_BASED_DIR64
entry.Type = 3 if elf.elfclass == 32 else 10
pe_reloc_blocks[block_rva].entries.append(entry)
continue
raise RuntimeError(f"Unsupported relocation {reloc}")
def convert_elf_relocations(
elf: ELFFile, opt: PeOptionalHeader, sections: typing.List[PeSection]
) -> typing.Optional[PeSection]:
dynamic = elf.get_section_by_name(".dynamic")
if dynamic is None:
raise RuntimeError("ELF .dynamic section is missing.")
[flags_tag] = dynamic.iter_tags("DT_FLAGS_1")
if not flags_tag["d_val"] & ENUM_DT_FLAGS_1["DF_1_PIE"]:
raise RuntimeError("ELF file is not a PIE.")
pe_reloc_blocks: typing.Dict[int, PeRelocationBlock] = {}
for reloc_type, reloc_table in dynamic.get_relocation_tables().items():
if reloc_type not in ["REL", "RELA"]:
raise RuntimeError("Unsupported relocation type {elf_reloc_type}.")
convert_elf_reloc_table(
elf, reloc_table, opt.ImageBase, sections, pe_reloc_blocks
)
if len(pe_reloc_blocks) == 0:
return None
data = bytearray()
for rva in sorted(pe_reloc_blocks):
block = pe_reloc_blocks[rva]
n_relocs = len(block.entries)
# Each block must start on a 32-bit boundary. Because each entry is 16 bits
# the len has to be even. We pad by adding a none relocation.
if n_relocs % 2 != 0:
n_relocs += 1
block.entries.append(PeRelocationEntry())
block.BlockSize = (
sizeof(PeRelocationBlock) + sizeof(PeRelocationEntry) * n_relocs
)
data += block
for entry in sorted(block.entries, key=lambda e: e.Offset):
data += entry
pe_reloc_s = PeSection()
pe_reloc_s.Name = b".reloc"
pe_reloc_s.data = data
pe_reloc_s.VirtualSize = len(data)
pe_reloc_s.SizeOfRawData = align_to(len(data), FILE_ALIGNMENT)
pe_reloc_s.VirtualAddress = align_to(
sections[-1].VirtualAddress + sections[-1].VirtualSize, SECTION_ALIGNMENT
)
# CNT_INITIALIZED_DATA|MEM_READ|MEM_DISCARDABLE
pe_reloc_s.Characteristics = 0x42000040
sections.append(pe_reloc_s)
opt.SizeOfInitializedData += pe_reloc_s.VirtualSize
return pe_reloc_s
def write_pe(
file, coff: PeCoffHeader, opt: PeOptionalHeader, sections: typing.List[PeSection]
):
file.write(b"MZ")
file.seek(0x3C, io.SEEK_SET)
file.write(PE_OFFSET.to_bytes(2, byteorder="little"))
file.seek(PE_OFFSET, io.SEEK_SET)
file.write(b"PE\0\0")
file.write(coff)
file.write(opt)
offset = opt.SizeOfHeaders
for pe_s in sorted(sections, key=lambda s: s.VirtualAddress):
if pe_s.VirtualAddress < opt.SizeOfHeaders:
# Linker script should make sure this does not happen.
raise RuntimeError(f"Section {pe_s.Name} overlapping PE headers.")
pe_s.PointerToRawData = offset
file.write(pe_s)
offset = align_to(offset + len(pe_s.data), FILE_ALIGNMENT)
for pe_s in sections:
file.seek(pe_s.PointerToRawData, io.SEEK_SET)
file.write(pe_s.data)
file.truncate(offset)
def elf2efi(args: argparse.Namespace):
elf = ELFFile(args.ELF)
if not elf.little_endian:
raise RuntimeError("ELF file is not little-endian.")
if elf["e_type"] not in ["ET_DYN", "ET_EXEC"]:
raise RuntimeError("Unsupported ELF type.")
pe_arch = {
"EM_386": 0x014C,
"EM_AARCH64": 0xAA64,
"EM_ARM": 0x01C2,
"EM_LOONGARCH": 0x6232 if elf.elfclass == 32 else 0x6264,
"EM_RISCV": 0x5032 if elf.elfclass == 32 else 0x5064,
"EM_X86_64": 0x8664,
}.get(elf["e_machine"])
if pe_arch is None:
raise RuntimeError(f"Unuspported ELF arch {elf['e_machine']}")
coff = PeCoffHeader()
opt = PeOptionalHeader32() if elf.elfclass == 32 else PeOptionalHeader32Plus()
# We relocate to a unique image base to reduce the chances for runtime relocation to occur.
base_name = pathlib.Path(args.PE.name).name.encode()
opt.ImageBase = int(hashlib.sha1(base_name).hexdigest()[0:8], 16)
if elf.elfclass == 32:
opt.ImageBase = (0x400000 + opt.ImageBase) & 0xFFFF0000
else:
opt.ImageBase = (0x100000000 + opt.ImageBase) & 0x1FFFF0000
sections = copy_sections(elf, opt)
pe_reloc_s = convert_elf_relocations(elf, opt, sections)
coff.Machine = pe_arch
coff.NumberOfSections = len(sections)
coff.TimeDateStamp = int(os.environ.get("SOURCE_DATE_EPOCH", time.time()))
coff.SizeOfOptionalHeader = sizeof(opt)
# EXECUTABLE_IMAGE|LINE_NUMS_STRIPPED|LOCAL_SYMS_STRIPPED|DEBUG_STRIPPED
# and (32BIT_MACHINE or LARGE_ADDRESS_AWARE)
coff.Characteristics = 0x30E if elf.elfclass == 32 else 0x22E
opt.AddressOfEntryPoint = elf["e_entry"]
opt.SectionAlignment = SECTION_ALIGNMENT
opt.FileAlignment = FILE_ALIGNMENT
opt.MajorImageVersion = args.version_major
opt.MinorImageVersion = args.version_minor
opt.MajorSubsystemVersion = args.efi_major
opt.MinorSubsystemVersion = args.efi_minor
opt.Subsystem = args.subsystem
opt.Magic = 0x10B if elf.elfclass == 32 else 0x20B
opt.SizeOfImage = align_to(
sections[-1].VirtualAddress + sections[-1].VirtualSize, SECTION_ALIGNMENT
)
opt.SizeOfHeaders = align_to(
PE_OFFSET
+ coff.SizeOfOptionalHeader
+ sizeof(PeSection) * max(coff.NumberOfSections, args.minimum_sections),
FILE_ALIGNMENT,
)
# DYNAMIC_BASE|NX_COMPAT|HIGH_ENTROPY_VA or DYNAMIC_BASE|NX_COMPAT
opt.DllCharacteristics = 0x160 if elf.elfclass == 64 else 0x140
# These values are taken from a natively built PE binary (although, unused by EDK2/EFI).
opt.SizeOfStackReserve = 0x100000
opt.SizeOfStackCommit = 0x001000
opt.SizeOfHeapReserve = 0x100000
opt.SizeOfHeapCommit = 0x001000
opt.NumberOfRvaAndSizes = N_DATA_DIRECTORY_ENTRIES
if pe_reloc_s:
opt.BaseRelocationTable = PeDataDirectory(
pe_reloc_s.VirtualAddress, pe_reloc_s.VirtualSize
)
write_pe(args.PE, coff, opt, sections)
def main():
parser = argparse.ArgumentParser(description="Convert ELF binaries to PE/EFI")
parser.add_argument(
"--version-major",
type=int,
default=0,
help="Major image version of EFI image",
)
parser.add_argument(
"--version-minor",
type=int,
default=0,
help="Minor image version of EFI image",
)
parser.add_argument(
"--efi-major",
type=int,
default=0,
help="Minimum major EFI subsystem version",
)
parser.add_argument(
"--efi-minor",
type=int,
default=0,
help="Minimum minor EFI subsystem version",
)
parser.add_argument(
"--subsystem",
type=int,
default=10,
help="PE subsystem",
)
parser.add_argument(
"ELF",
type=argparse.FileType("rb"),
help="Input ELF file",
)
parser.add_argument(
"PE",
type=argparse.FileType("wb"),
help="Output PE/EFI file",
)
parser.add_argument(
"--minimum-sections",
type=int,
default=0,
help="Minimum number of sections to leave space for",
)
elf2efi(parser.parse_args())
if __name__ == "__main__":
main()
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